| Date | May 2019 | Marks available | 2 | Reference code | 19M.3.HL.TZ1.19 |
| Level | Higher level | Paper | Paper 3 | Time zone | 1 |
| Command term | Describe | Question number | 19 | Adapted from | N/A |
Question
Describe the mechanism of formation of type I a supernovae.
Describe the mechanism of formation of type II supernovae.
Suggest why type I a supernovae were used in the study that led to the conclusion that the expansion of the universe is accelerating.
Markscheme
ALTERNATIVE 1
a white dwarf star in a binary system accretes mass from the companion star ✔
when the white dwarf star mass reaches the Chandrasekhar limit the star explodes «due to fusion reactions»✔
ALTERNATIVE 2
it can be formed in the collision of two white dwarf stars ✔
where shock waves from the collision rip both stars apart ✔
a red supergiant star explodes when its core collapses ✔
«it was necessary» to measure the distance «of very distant objects more accurately» ✔
type I a are standard candles/objects of known luminosity ✔
Examiners report
Supernova. The mechanism of the formation of supernovae Ia was well described by many candidates.
In (ii), for the description of the mechanism of type II supernovae, many responses lacked detail and did not make mention of core collapse.
Part b) was well answered by most of the prepared candidates with a good understanding that these stars behave as “standard candles”.
